Aluminum compounds



June 27, 1961 c. R. coNARD ETAL ALUMINUM COMPOUNDS Filed Jan. 27, 1958W@ (gew,

Il m y M #l/ O OO O@ O ON O@ Om O? Om ON O wmPDZIZ 7: m k I ONFZOOUnited States Patent a 2,990,247 ALUlVDNUM COMPOUNDS Charles R. Cunard,Ferguson, Mo., and John F. Lemp, Alton, lll., assignors to MallinckrodtChemical Works, St. Louis, Mo., a corporation of Missouri Filed Jan. 27,1958, Ser. No. 711,208 5 Claims. (Cl. 23-110) This invention relates tonovel aluminum compounds, and more particularly to magnesium aluminumsilicates.

Briey the present invention is directed to novel magnesium aluminumsilicates corresponding to about the empirical formula:

where z is a number such that the loss on ignition of the composition isnot less than approximately 20% by weight; and to methods for thepreparation of said compositions.

Among the objects of the present invention are the provision of basicmagnesium aluminum silicate compositions having improvedacid-neutralizng properties; the provision of compositions of thecharacter described which retain their reactivity indefinitely undernormal storage conditions; the provision of compositions of thecharacter described which combines high neutralizing capacity withsuperior buffering ability, and the provision of methods for preparingcompositions of the character described. Other objects of the inventionwill be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the products and methods hereinafterdescribed, the scope of the invention being indicated in the followingclaims.

Aluminum hydroxide gel and magnesium trisilicate have been employedindividually and in admixture for'the purpose of neutralizing excessacid in the stomach and for other purposes. 0f the two, freshly preparedaluminum hydroxide gel has the greater neutralizing capacity. However,on drying and/ or during storage it rather rapidly loses its capacityand for that reason its eicacy and therefore its usefulness soondeteriorates. Moreover, it has an undesirable constipative effect. Tooffset this latter effect, aluminum hydroxide gel is sometimes mixedwith magnesium trisilicate, a mild laxative. Such mixtures, however, areno more stable than aluminum hydroxide alone L and also deteriorate onstorage. If used in excess, magnesium trisilicate alone permits amaximum pH above 6 whereas a maximum pH of 3-4 is generally considereddesirable.

K According to the present invention, a precipitated magnesium aluminumsilicate may be prepared which has the desirable acid neutralizingproperties of freshly prepared aluminum hydroxide gel-magnesiumtrisilicate mixtures but which, surprisingly, retains its activityindefinitely under normal storage conditions.

In its preferred embodiment the precipitated magnesium aluminum silicatecomposition of the present invention corresponds to the empiricalformula However, these proportions may be varied within certain limitswithout losing the essential advantages of the present invention. `Forexample, the proportion of aluminum may be varied in the formula from0.65 A1303 to 1.3. Below about 0.65 A1203 the buffering effect of thecomposition is poor and the acid-consuming capacity is low. Above about1.3 A1203 the product becomes undesirably bulky, and the acid-consumingcapacity is adversely affected.

i The compositions of the present invention are designated asprecipitated magnesium aluminum silicates to distinguish them fromnaturally occurring silicates con- 2,990,247 Patented June 27, 1961 ICEtaining both magnesia and alumina which are essentially inactive, andfrom the previously known mixtures of aluminum hydroxide and magnesiumtrisilicate which deteriorate on storage.

The precipitated magnesium aluminum silicates of the present inventionare prepared by combining a stoichiometric quantity of a solublealuminum salt, such as aluminum sulfate, an excess of a solublemagnesium salt such as magnesium sulfate, and a quantity of an alkalimetal silicate solution containing a stoichiometric quantity of Si02 anda quantity of alkali metal oxide equivalent to the sum of the desiredamounts of Mg0 and A1203 in the final product. The physical form of theprecipitated magnesium aluminum silicate may then be improved by heatingthe resulting slurry and allowing it to age. If desired, the magnesiumaluminum silicate may be dried at temperatures not exceeding about C.

The proportions of the components in the compositions of the presentinvention are easily controlled by regulating Ithe proportions of thereactants. The proportions of alumina and silica are determined by theamounts of aluminum salt and sodium silicate added to the reactionmixture. An excess of magnesium ions in the iinal mixture is preferableto an excess of caustic. Therefore, the magnesia content is preferablydetermined by the amount of caustic used; i.e., the amount of caustic,including that from the sodium silicate solution, should be equivalentto the sum of the alumina and magnesia contents. For example, in aproduct to contain 2 mols of MgO and 1 mol A1203, the total amount ofcaustic should be equivalent to 5 mols of NaZO. A sufficient excess ofmagnesium ions is then added to insure complete reaction.

The manner and order of combining the reactants may be varied over awide range. The primary effect of such variations is on the physicalcharacteristics of the product such as uniformity, bulk, and particlesize, while the fundamental chemical characteristics such asacid-neutralizing capacity, buffering action, and stability of theproduct with respect to these characteristics, which are primarily afunction of chemical composition, are relatively unaffected.

The precipitation of the magnesium aluminum silicate 1's preferablycarried out in a reaction mixture having a -pH greater than 7 in orderto avoid the inclusion of basic sulfates which are rather insoluble anddifficult to remove by Washing. Therefore, the magnesium and aluminumsulfates, solutions of which salts are acid in character, are preferablyadded to the alkaline silicate solution, rather than the reverse.

In place of the sulfates of magnesium and aluminum, other commonWater-soluble salts of these metals such as thechlorides, nitrates andacetates may be used. Still other halides or organic acid salts might beused, but these are less common, more expensive, and do not oiier anyadvantages.

The concentrations of the reactants are not critical. It is usually mosteicient to carry out the reactions at the ygreatest concentrations whichwill provide a fluid and easily stirred reaction mixture. More importantis the rate at which the reactants are combined. To obtain maximumuniformity and optimum physical properties, the magnesium and aluminumsalts should Ibe combined slowly with the sodium silicate and witheicient stirring. Rapid combination of concentrated solutions withinadequate stirring tends to produce impure, non-uniform products.

Y The aluminum sulfate may be added either before or after the magnesiumsulfate or the two may be added together.

other, or there may be a delay in order to per-mit the intermediateprecipitate to age. Aging: the intermediate product under substantiallyneutral conditions tends' to give less bulky final products, whereasaging the intermediate product in the presence of excess alkali tends tohave the opposite effect.

The precipitation is preferably carried out at temperatures notexceeding 50 C. since at higher precipitation temperatures the acidneutralizing activity of the product tends to be adversely affected.Once precipitation of the final product is complete, the temperature maybe increased to 70-90 C. for a period of time without harm to theproduct unless such heating is unduly prolonged. In many cases it hasbeen found that such a heating or aging period has a desirable eiect onthe physical characteristics ofthe precipitate, primarily in making iteasier to iilter and wash.

If desired, the precipitated magnesium aluminum silicates of the presentinvention may -be dried at temperatures not substantially in excess of100 C. without harm to their acid-consuming capacity, or the productsmay be used as aqueous suspensions after removing the watersolubleby-products of the reaction. lf dried, a loss on ignition ofapproximately 20% by weight is the minimum which can be attained withoutemploying drying temperatures that would be deleterious to the product.

The precipitated magnesium aluminum silicates of the present inventionare useful wherever it is desired to neutralize excess acid, especiallywhere the amount of acid to be neutralized is indefinite and an excessof base must be added without producing an alkaline condition. They are,therefore, particularly useful for neutralizing excess acid in thestomach. Their acid-consuming capacity is intermediate between that offreshly precipitated aluminum hydroxide gel and magnesium trisilicateand generally exceeds the capacity of dried aluminum hydroxide gel whichhas :been stored, any length of time. The precipitated magnium aluminumsilicates of the present invention may be used as active ingredients ineither solid or liquid preparations for the treatment of excess stomachacidity, and they may be used alone or in combination with otherchemically compatible, non-acidic ingredients.

'I'he precipitated magnesium aluminum silicates are much superior toaluminum hydroxide gel and 4mixtures containing aluminum hydroxide gel,ywith. respect to stability. As is well-known, aluminum hydroxide gel,especially in the d-ry form, steadily decreases in activity with time.Its storage life is, therefore, relatively short. The precipitatedmagnesium aluminum silicates, on the other hand, show no evidence of anydecreasein activity on storage, either in dry or liquid form. This issurprising since in most respects they are comparable to. a mi'xtu-re offreshly prepared aluminum hydroxide gel with magnesium trisilicate.

Precipitated magnesium aluminum silicates are also clearly superior tomagnesium trisilicate with respect to buifering qualities. Not only dothey exert their buffering eifect for a longer period of time, but themaximum pH is in the neighborhood of 3-4 rather than 6-7 as in the caseof magnesium trisilicate. 'While precipitated. magnesium aluminumsilicate is comparable to freshly prepared mixtures of active aluminumhydroxide gel and magnesium trisilicate, the buffering qualities of thelatterv steadily deteriorate with time owing to the decrease in theactivity of the aluminum hydroxide. Precipitated magnesium aluminumsilicate, on the other hand, retains its excellent bulferingcharacteristics indenitely.

The following examples further illustrate the invention.

Example 1 To 0.96 liter of a well` stirred solution of sodium silicate(116 1g. Nat-2O and 168 g. Si02 per liter) was added 0.625 liter ofmagnesium sulfate solution (314.6` g.

MgSO4 per liter) dropwise over a periodi ofabout 90'.

minutes and at a temperature of about 35"V C. To this 2,990,247 l vnslurry 0.91 liter of sodium hydroxide solution (237.345. NaOH per liter)was addedrapidly with stirring, followed immediately by 1.047 liters ofaluminum sulfate solution (570.4 g. A12(SO4)318H2O per liter) over aperiod of approximately minutes. Finally, another 0.1 liter of themagnesium sulfate solution was added to insure: an excess. Stlrringy wascontinued and the slurry was warmed to 70 C., and left to standovernight at 65-70 C. The magnesium aluminum silicate was then tiltered,Washed, dried at 65- C. until the loss on ignition was 28%, and thenfinely milled. The molar ratio of A1203 to MgO in this product wasapproximately 1:2 and the molar ratio of A1203 to Si02 wasapproximately'123. Bulks ofl 50-90 1i. oz. per lb. are typical.

Example 2 A caustic silicate solution was prepared by dissolving 197 g.of sodium4 hydroxide in 1.024 liters of sodium silicate solution (116 g.Na2O and 168 g. SiO2 per liter) and diluting to a density otv 27.7l B.

A solution of aluminum sulfate was prepared by dissolving 547l g. of'Al2(SO4)3l8'H2O in 1.024 liters of water and to this was added 0.665liter of a magnesium sulfate solution (314.6 g. MgSO4 per liter).

The aluminum sulfate-magnesium sulfate was thenadded dropwise withstirring over a period of about-v4` hours to the caustic sodium silicatesolution at a temperature of 3'5" C. An additional 0.1 liter ofthemagnesium sulfate solution was added and the temperature was slowlyraised to 65-7 0 C'. with continued stirring. After two hours,4 thesolution was allowed to stand at 75 C. overnight withoutv stirring andthen for several days at room temperature. The magnesium aluminumsilicate was then ltered off, washed, dried at about 65 C. until theloss on ignition was 26%, and then finely milled. The molar ratio ofA1203 to M'gO in this product was approximately 0.8612.

In order to obtain a product in which the molar ratio of A1203 to MgO is1:2, the amount of sodium hydroxide dissolvedv in the sodium silicatesolution should be increased to 229 g. and the amount of aluminumsulfate used' should be increased to 637 g. A12(SO4)318H2O; The bulkv ofthe product is typically 50-60 oz. per lb.

Example 3 Example 1 was repeated except that the magnesium silicateslurry w-as heated' to 70 C; and then allowed to-cool and stand for 24hours before the addition of the sodium hydroxide and aluminum sulfatesolutions. This methodl tends to give a somewhat more dense product thanthe method of' Example l, but otherwise products are` comparable.

Example 4 Example; l was repeated.. except that the; magnesium silicate.slurry was; allowed. toA age for 24 hours. after theV addition. of thesodium` hydroxide solution and4 before the. addition of the. aluminumsulfate solution. Thsmodication causes a large increase, in bulk (bulksof over fl. oz. per lb. arey typical).

Example 5 To 0.96 liter of a solution of sodium silicate (116 g. Nag()and 168 g. SiOZ per liter) at a temperature of about 35'vcr C5 was added0.311 liter of sodium hydroxide soluf tion (23713 g. NaOH per liter)rapidly with stirring fol- A130, to SiO, was approximately 1:3. Theproduct obtained by this method of preparation is of medium high bulk,intermediate between the products obtained by the methods ofExamples 1and 4, and shares the same excellent antacid properties. 5 the methoddescribed in Example 7. At the end of the Example 6 storage test theduration was 123 minutes and the peak pH was 3.51. The following methodwas used to determine the acid Example' 9 consuming capacity of theproducts of the present inven- P d al .1. d f tion and compare them withthe substances and mixtures l() re.c1p1t3.te magnesium ummum Sl Pateprepre as employed heretofo described in Example 1 was compared with twodilerent The acid consuming capacity of the product described plpfsfcalmlxmrs alummum hydroxlde.and ,magnesium in Example 1 was measured bydetermining the weight of trlslhgate following the prqdure descnbed mExample antacid required to neutralize 340 m1. of 0.1 N hydro- 7' Tim.rst mixture qeslgnated A .was RrPared by chloric acid to a pH of 2.8.This is an approximation comllnng aqueou? Slurnes of nagneslum tnslhcateof the conditions encountered in actual use when the subpreclpltaitedalumnium hydroxlde and, then Seriamtmg stanceis used to correct excessstomach acidity. The re and drying the solids' T h? second Htlxture..dslgnated sultn'g value can be designated as the equivalent dose B WISPrepared b y drymixing magnesium trisilioate and fr purposes ofcomparing it with other antacid Sub aluminum hydroxide dried gel. Inaddition to determinstances 20 ing the duration of pH control, the timerequired to raise i Typical valus' for the equivalent dose for magnesiumthe pH of the 0.1 N hydrochloric acid from l to 3 wasaluminum silicateand other analogous substances were also determmed found to be asfollows.

' Time to Time to Duration Material Percent pH 2, pH 3, of pH MaterialEqulva- A1102 min. min. control, lent Dose minutes Preeipltatedmagnesium aluminum silicate moisture) Magnesium aluminum silicate i. 78(30% moisture) 2o 0. 5 1 12o Undrled aluminum hydroxide gel. g 1.10Mixture A 22 0.5 1 106 Commercial mixtures of aluminum hydroxide gel andmag- 30 Mixture B 20 1 3 94 nesium trisiiicete g 11.16-2. 36 Aluminumhydroxide gel eo i 2 viis Magnesium trisilicate 2. 96 Magnesiumtrlsilicate powder.. 0 0. 5 i 104 Me esium carbonate 1. 59Commercialmixtures ofalumi- So umbicarbonate-.. 2.60 num hydroxide geland Magnesium hydroxide- 0.99 magnesium trlsillcate:

et 2 12 1 Based on activo ingrdients. "nosed on total weight theequivalent 35 zofo 5 io 9s dose ranges from 1.77-4.72 g.

if "I Elfample 7 The exact structure of the precipitated magnesium Thebuffering elfeet of magnesium aluminum silicate aluminum silicates ofthe present invention is not clear, was measured and eompared with otherentaeld Sub. however, the available evidence all indicates that thestances in the following manner; 40 components are chemically bound andare not present An equivalent dose of the substance to be tested,determelely 'as a Physlcal mlXlufe- T] 1e Stablmy 0f the CCIP* mined asin Example 6, was added to 100 mL of oonpositions is perhaps the moststriking evidence for this, stantly stirred 0.1 N hydrochloric acidmaintained nl a but there are also other indications. There are smallbut temperature of 37.5i0.5 C, A few drops 0f n wetting significantdifferences in the infrared absorption spectra agent was added to insurethorough wetting of the sain- 0f P1' CCIPated magIlPSiUm alumlnumsilicate and PhYS ple. The pH was determined at the end of 1, 3, 5 andcal mixtures of aluminum hydroxide and magnesium tri- 10 minutes afteraddition of the sample and at the end silicate 'Whether Prepared by Wet01' dry methods- This of each 10 minute period thereafter, After each 10evidence, while not conclusive, strongly suggests a chemminute pHreading, 2 inl. of 1.0 N hydrochloric acid was ical bond between aluminaand silica in the compositions added. Observations were continued untilthe pH dropped of the present invention. Magnesium aluminum silicatebelow 2- prepared according to the preferred conditions of the Thebuiering effects of the test compounds were compresent invention so asto preclude the incidental formapared in terms of duration of pH controland the peak tion of inactive A1203, is substantially completely solublepH developed during the test. in N/ 10 hydrochloric acid. Physicalmixtures do not .55 dissolve completely. Precipitated magnesium aluminumDuration silicate of the present invention will continue to hydrateSubstance ofitil1 peak pH or dehydrate, depending upon -atmosphericconditions, ges without any significant change in its chemicalproperties when compared on an anhydrous basis. Finally, the time Preciitated magnesium aluminum silicate (30% 60 required to raise the p H ofa N/ l0 hydrochloric acid Ulieiiduirsaianau::i::31:: lig 13 Solflonfron? 1 t?? 1S Shorter ff PfFCPltated mlg Commercial mixtures otaiuminumhydroxide gel nesium aluminum silicate than for aluminum hydroxideMlglgelslillffcgtljtef- 3o-g2 35g@ gel alone or physical mixtures ofaluminum hydroxide Megnesium earbonete "I iso 717 gel and magnesiumtrisilicate. fgnufagg While it is to be taken only in an illustrativeand not in a limiting sense, the properties of the precipitatedmagnesium aluminum silicates of the present invention are FIGURE 1 showsa typical neutralization cilrve for best accounted for by the followingformula: the precipitated magnesium aluminum silicate of the presentinvention compared with a similar curve for alumi- 2Mg0'2A1O(OH)35102'XII2O num hydroxide in admixture with magnesium trisilicate. Wherex is ,approximately 7, but may vary with atmos- Example 8 phericconditions. In view of the above, it will Ibe seen that the several Thestability of magnesium aluminum silicate was objects of the inventionare achieved and other advandemonstrated as follows: Samples ofmagnesium alumitageous results attained.

num silicate prepared as described in Example l were suspended indistilled water and stored for a period of live months. Initially theduration of pH control was 122 min. and the peak pH was 3.49, whendetermined by As various changes could be made in the above methods andproducts without departing from the scope of the invention, it isintended that. all matter contained in the above description or .shownin the accompanying drawing; shall be interpreted as illustrative and.not in a limiting sense.

We claim:

1. The method of making a precipitated magnesium aluminum silicate ofabout the following empirical formula:

where z' is a number such that the loss on ignition of the compositionis not less than approximately 20% by weight, which comprises graduallyadding ak solution of magnesium sulfate to a solution of sodium silicateat. a temperature not exceeding approximately 50 C. the said silicatesolution containing` silica and alkali in the proportions 3Si02z2Na2Oand the` said magnesiumV sulfate solutiony containing suicient MgSO'.,lto react. with a major proportion but less than all of thev alkali inthe sodium silicate solution; adding additional alkali tothe reactionmixture in the proportions of 3 mols of Na20 for each mol of SiO2 in thereaction mixture; thereafter adding aluminum sulfate solution in anamount corresponding to approximately 1 mol A1203 for each 3 mols ofSi02 present in the reaction mixture; adding, additional magnesiumsulfate solution suilicient to provide an excess of magnesium ions overthose required to complete. the reaction; increasing the temperature toapproximately 65-70" C. to complete the reaction; and thereafterrecovering the precipitated magnesium aluminum silicate.

2. A precipitated magnesium aluminum silicate of about the followingempirical formula:

' A1303' Ssiog ZHo where z is a number such that the loss on ignition ofthe composition is not less than approximately 20% 'by weight.

3. A precipitated magnesium aluminum silicate fcorre- 5. The method ofmakingA a precipitated magnesium aluminum silicate substantiallycorresponding to` the empirical formula:

where z is a number such that the loss on ignition ofthe composition isnot less than approximately 20% by weight, which comprises combining inaqueous solution an alkali metal silicate containing .a known. quantityof Si02 and an amount of alkali metal oxide chemically equivalent to therequired amounts of A1203 and MRO; a quantity of a soluble aluminumsal't equivalentV to the required amount of A1203 and a quantity of asoluble magnesium salt in excess of that necessary to provide therequired amount of MgO and separating the precipitated magnesiumaluminum silicate from the reaction mixture;

References Cited in the tile of thisv patent UNITED STATES PATENTSk1,087,705 Allen Feb. 17, 1914'- l,759,919 Singer MayZT, 1930 2,540,689Porret Feb; 6, 1951 OTHER REFERENCES Strotzer: German patent'application, G 8505,

rub- IiShed oet. 27, 1955,.C1ass son the lines 71 and 72 for (570A gA12(SO)318H UNITED STATES PATENT OFFICE o CERTIFICATE OF CORRECTIONPatent No. 2,990,124? June 27u` 1961 Charles R., Conard et al., n t yvIt is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below Column 1q line 151 for "MgOeyA'12O33SO2ZH2O read2MgOA12O33SiO2zH2O --3 line 26, for "Combines" read combine column Ieline 50v after "otherwise" insert 2O per liter) of about 90 minutes"read (314.6 g., MgSOlc per liter) over a period of about 90 minutescolumn 8 line 23w for "Mg0. read lVIgOv Signed and sealed this 21st -dayof November 1961.,

(SEAL) Attest: n

ERNEST W. SWIDER DAVID L. LADD y Attesting Officer Commissioner ofPatents USCOMM-DC

1. THE METHOD OF MAKING A PRECIPITATED MAGNESIUM ALUMINUM SILICATE OFABOUT THE FOLLOWING EMPIRICAL FORMULA: 2MGO.AL2O3.3SIO2.ZH2O